C4 2005 Fault code C1302 - A lot of stuff replaced

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lunarband
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Joined: 14 Jun 2021, 21:53

C4 2005 Fault code C1302 - A lot of stuff replaced

Post by lunarband »

Hello. We have been working on a -05 petrol C4 and currently we are running into fault code C1302. The full description in Diagbox is C1302 Incoherence between the brake light switch and the pressure sensor; short circuit, short circuit to ground or open circuit

The fault can be wiped, but reappears on every engine start. Beeps, ABS light lights up and "Braking system faulty" can be seen on the screen. Looking at the live data the brake pressure is like it should be, so are the wheel sensor data. You can drive the car.

What we've done so far:
  • Replaced the ABS ECU
  • Replaced the ABS pump
  • Tried two different brake light switches
to no avail. We are suspecting the wiring between the brake light switch and the ABS unit. How would one go about measuring / identifying any damaged wires there? Are there resources available on the wire color coding?
Last edited by lunarband on 27 Jun 2021, 11:37, edited 2 times in total.
wheeler
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by wheeler »

I woldnt have thought a 2004 model C4 would have a brake pressure sensor or is this a bad translation?
If you post the VIN i can look out an ABS wiring diagram.
lunarband
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by lunarband »

wheeler wrote:
15 Jun 2021, 02:18
I woldnt have thought a 2004 model C4 would have a brake pressure sensor or is this a bad translation?
If you post the VIN i can look out an ABS wiring diagram.
This is the VIN we've got. VF7**************[VIN obfuscated, can be read by forum staff]
It says 2007 but the car has been registered since 2005.
wheeler
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by wheeler »

The Brake switch is item 2021
Attachments
InkedC4_ESP_LI.jpg
Last edited by wheeler on 15 Jun 2021, 15:43, edited 1 time in total.
wheeler
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by wheeler »

As i suspected there doesn't seem to be a braking pressure sensor on this car unless it's an integral part of the ESP block?
Normally brake pressure sensors are externally screwed into either the brake master cylinder or directly into the ABS block.
lunarband
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by lunarband »

wheeler wrote:
15 Jun 2021, 13:53
As i suspected there doesn't seem to be a braking pressure sensor on this car unless it's an integral part of the ESP block?
Normally brake pressure sensors are externally screwed into either the brake master cylinder or directly into the ABS block.
Yes. It's integrated on the hydraulic block as far as I know. Changing the hydraulic block made the idle brake pressure report 0 like it should instead of 4.

Is 2120 what you meant? It's a bit difficult to make out the numbers off that image, but thank you anyway. Any resources on the color coding?
wheeler
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by wheeler »

2120 is the brake position switch. Citroen don’t go by colours, the go by codes printed on the wires. You can see them on the diagram but you may need to zoom in.
lunarband
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by lunarband »

wheeler wrote:
15 Jun 2021, 14:49
2120 is the brake position switch. Citroen don’t go by colours, the go by codes printed on the wires. You can see them on the diagram but you may need to zoom in.
Can't find item 2021 on the diagram.
wheeler
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by wheeler »

Its 2120 not 2021.
I have edited the diagram to highlight it.
lunarband
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by lunarband »

wheeler wrote:
15 Jun 2021, 15:44
Its 2120 not 2021.
I have edited the diagram to highlight it.
Yeah, found that already. Thanks! Got confused by your previous post.
wheeler wrote:
15 Jun 2021, 13:50
The Brake switch is item 2021
So, should the wires have a 2- or 4-digit number marked on them?
wheeler
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Re: C4 2004 Fault code C1302 - A lot of stuff replaced

Post by wheeler »

Wire codes are normally anything from 2 - 6 digits & can contain letters and numbers
Pin 1 of the brake switch is BE10A and pin 2 is 210B.
The bit that says 4V VE means its a 4 way green connector.
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GiveMeABreak
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Re: C4 2005 Fault code C1302 - A lot of stuff replaced

Post by GiveMeABreak »

Ok, as per your PM:
Fault Code: C1302 Braking pressure sensor signal fault: Open circuit, short circuit to positive, short circuit to earth
Description of Fault:The supply voltage of the pressure sensor inside the ESP ECU is monitored every 40 milliseconds.
The supply voltage of the pressure sensor inside the ESP ECU is monitored every 40 milliseconds
Possibility 1
The output voltage from the pressure sensor is outside the authorised range.

Possibility 2
The supply voltage of the pressure tester is not within the nominal range.
Conditions for Fault to clear: Possibility 1
The output voltage from the pressure sensor inside the ESP ECU is within the authorised range.
Possibility 2
The supply voltage of the pressure sensor is within the nominal range.
Downgrade Modes whilst Fault is active:
  • The ABS operation that is current goes its term. Once it is finished, cutting of all ABS operations.
  • Immediate cutting of all the speed control functions (Electronic stability control (ESP))
  • The electronic brakeforce distribution function is in down-grade mode
Symptoms: Lighting of the ABS and ESP warning lamps
Suspect Areas:
  • Pressure sensor inside the ESP ECU
  • Presence of air bubbles in the ESP hydraulic block
  • Brake light switch
  • Connectors
  • Electrical harnesses
  • Fuses
Wiring Diagrams

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